T1218.010: Regsvr32
Adversaries may abuse Regsvr32.exe to proxy execution of malicious code. Regsvr32.exe is a command-line program used to register and unregister object linking and embedding controls, including dynamic link libraries (DLLs), on Windows systems. The Regsvr32.exe binary may also be signed by Microsoft.
Malicious usage of Regsvr32.exe may avoid triggering security tools that may not monitor execution of, and modules loaded by, the regsvr32.exe process because of allowlists or false positives from Windows using regsvr32.exe for normal operations. Regsvr32.exe can also be used to specifically bypass application control using functionality to load COM scriptlets to execute DLLs under user permissions. Since Regsvr32.exe is network and proxy aware, the scripts can be loaded by passing a uniform resource locator (URL) to file on an external Web server as an argument during invocation. This method makes no changes to the Registry as the COM object is not actually registered, only executed. This variation of the technique is often referred to as a "Squiblydoo" and has been used in campaigns targeting governments.
Regsvr32.exe can also be leveraged to register a COM Object used to establish persistence via Component Object Model Hijacking.
Positive Technologies products that cover the technique
MaxPatrol SIEM knowledge base
mitre_attck_defense_evasion: PT-CR-946: Suspicious_Execution_Via_Regsvr32: An attempt to bypass application-start restrictions by using regsvr32.exe (a built-in Microsoft Windows utility used for DDL registration) mitre_attck_defense_evasion: PT-CR-650: Suspicious_File_Created_By_Legal_Process: Detects creation of suspicious files by legitimate processes mitre_attck_defense_evasion: PT-CR-198: Regsvr32_AWL_Bypass: An attempt to bypass application-start restrictions by using regsvr32.exe (a built-in Microsoft Windows utility used for DDL registration) hacking_tools: PT-CR-357: Koadic_REGSVR32_Stager: Possible use of the Koadic software with Regsvr32 is detected
Detection
ID | DS0011 | Data source and component | Module: Module Load | Description | Monitor DLL/PE file events, specifically creation of these binary files as well as the loading of DLLs into processes. Look for DLLs that are not recognized or not normally loaded into a process. Note: This looks for unsigned images that may be loaded by regsvr32, while attempting to eliminate false positives stemming from Windows/Program Files binaries. Analytic 5 - Loading Unsigned Images
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ID | DS0017 | Data source and component | Command: Command Execution | Description | Command arguments used before and after the regsvr32.exe invocation may also be useful in determining the origin and purpose of the script or DLL being loaded. |
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ID | DS0029 | Data source and component | Network Traffic: Network Connection Creation | Description | Monitor for newly constructed network connections that are sent or received by untrusted hosts. |
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ID | DS0009 | Data source and component | Process: Process Creation | Description | Use process monitoring to monitor the execution and arguments of regsvr32.exe. Compare recent invocations of regsvr32.exe with prior history of known good arguments and loaded files to determine anomalous and potentially adversarial activity. Note: Event IDs are for Sysmon (Event ID 1 - process create) and Windows Security Log (Event ID 4688 - a new process has been created).
Analytic 1 - Generic Regsvr32
Analytic 2 - Squiblydoo
Analyt 3 - New Items since last month
Analytic 4 - Spawning Child Processes
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Mitigation
ID | M1050 | Name | Exploit Protection | Description | Microsoft's Enhanced Mitigation Experience Toolkit (EMET) Attack Surface Reduction (ASR) feature can be used to block regsvr32.exe from being used to bypass application control. Identify and block potentially malicious software executed through regsvr32 functionality by using application control tools, like Windows Defender Application Control, AppLocker, or Software Restriction Policies where appropriate. |
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